1. Field of the Invention
The present invention relates to an image forming apparatus including a platen glass face provided in an apparatus body and having a reading area for reading a document set under a stationary condition thereof and an automatic reading area for reading the document while the document is guided past over this automatic reading area by an automatic document feeding mechanism, a cover means mounting the automatic document feeding mechanism and attached to the apparatus body via a pivot shaft to be pivoted for selectively opening/closing the platen glass face, and a reading guide attached to the cover means and configured for guiding the document in opposition to the automatic reading area when the cover means is closed.
2. Description of the Related Art
As an image forming apparatus of the above-noted type, there is known an apparatus in which the reading guide is immovably fixed to the cover means (see. e.g. Japanese Patent Application “Kokai” No. 2002-189319) (this conventional apparatus will be referred to as “First Prior Art” hereinafter).
As such image forming apparatus, there is known another apparatus as shown in FIG. 13 in which the reading guide 4b is attached to the cover means 4 via urging means 11 provided respectively at opposed ends thereof, so that this entire guide 4b can move to and away from the cover means 4 (see e.g. Japanese Patent Application “Kokai” No. 2001-235909) (this conventional apparatus will be referred to as “Seconds Prior Art” hereinafter).
With the above-described image forming apparatus, in order to be able to accurately read an image on a document while an automatic document feeding mechanism guides the document onto a platen glass face and then guides it through an automatic reading area provided on this face, it is essential that the platen glass face and the reading guide be maintained with a constant distance therebetween over the entire right/left width of the document, in particular, the document being fed be free from any force which may result in displacement thereof to either side.
According to First Prior Art described above, the reading guide is fixed (immovable) to the cover means. Therefore, in order to maintain such proper positional relationship between the platen glass and the reading guide, extremely high precision is required in their positional relationship for avoiding error in the attaching position of the cover means relative to the apparatus body.
In practice, however, due to e.g. the dimensional tolerance of a pivot shaft for the cover means and other parts associated therewith, it is difficult to realize such high precision attachment which maintains a same distance between the apparatus body (platen glass) and the cover means (reading guide) over all portions thereof. As a result, there tends to occur a problem of a portion of the reading guide (in particular, the portion thereof adjacent the pivot shaft) being afloat the platen glass face.
On the other hand, according to Second Prior Art described above, the reading guide is mounted such that the guide, in its entirety, is urged against the platen glass face by the urging means. Therefore, when the cover means is closed, the reading guide can readily assume a posture along the platen glass face. Hence, for example, when the image of the document is read at the automatic reading area with using the automatic document feeding mechanism, an appropriate gap can be maintained therebetween over all portions thereof. On the other hand; however, if the urging force of the urging means is large, this urging force will tend to push the cover means up away from the platen glass. As a result, the distal end portion of the cover means away from the pivot shaft may be pushed afloat the platen glass surface. Then, when the document reading operation is effected by manually placing and keeping the document still at a reading area on the platen glass face, without using the automatic document feeding mechanism, such “floating” cover means may cause a problem in the document reading operation.
Further, the reading guide employed in Second Prior Art is designed to be attached to the cover means with using screws. This fact makes the assembly of the apparatus troublesome and also requires a tool for fixing the screws. And, once the reading guide has been fixed with the screws, the reading guide will not normally be removed. Therefore, when there occurs change in the type and/or thickness of paper sheet material employed, the construction of Second Prior Art can only provide a same urging force to the paper sheet, regardless of its type/thickness.